The present invention relates to a flame retardant polyamide resin composition, and particularly to a flame retardant polyamide resin composition suitably usable for parts such as connectors, breakers, magnetic switches, etc. in the electrical and electronic fields and electronic parts in the field of automobiles. Furthermore, the present invention relates to a flame retardant reinforced polyamide resin composition which is very high in flame retardancy, does not generate corrosive hydrogen halide gases at the time of burning and has both excellent electric characteristics and excellent molding processability.
Hitherto, polyamide resins have been used in the fields of automobile parts, mechanical parts, electric and electronic parts, etc. because of their excellent mechanical strength, heat resistance, etc. However, in the recent uses for electric and electronic parts, the level of requirement for flame retardancy is increasing, and the flame retardancy is required to be much higher than the self-extinguishing properties which the polyamide resins possess inherently. Therefore, intensive investigations have been conducted on increasing the flame retardancy level to meet the UL94V-0 standard of Underwriters Laboratories, and generally it has been attempted to improve flame retardancy of polyamide resins by adding halogen-based flame-retarding agents or triazine-based flame-retarding agents to polyamide resins.
For example, there are known the addition of chlorine-substituted polycyclic compounds to polyamide resins (JP-A-48-29846), addition of bromine-based flame-retarding agents such as decabromodiphenyl ether (JP-A-47-7134), addition of brominated polystyrene (JP-A-51-47044, JP-A-4-175371), addition of brominated polyphenylene ether (JP-A-54-116054), addition of brominated cross-linked aromatic polymers (JP-A-63-317552), addition of brominated styrene-maleic anhydride polymers (JP-A-3-168246), etc. Compositions obtained by adding these halogen-based flame-retarding agents to glass fiber-reinforced polyamide resins have high flame retardancy and high stiffness, and, hence, have been widely used for electric and electronic parts, especially, connectors mounted on or connected with printed circuit laminates. However, halogen-based flame-retarding agents are believed to generate highly corrosive hydrogen halide gases and smoke or to generate toxic materials at the time of combustion, and because of these environmental problems, there is a trend to inhibit the use of plastic products containing the halogen-based flame-retarding agents.
Under the circumstances, triazine-based flame-retarding agents free of halogen have been noted and various investigations have been made on these flame-retarding agents. For example, there are well known a method of using melamine as a flame-retarding agent (JP-B-47-1714), a method of using cyanuric acid (JP-A-50-105744), and a method of using melamine cyanurate (JP-A-53-31759). Non-reinforced polyamide resin compositions obtained by these techniques have a high flame retarding level meeting the requirements of the UL94V-0 standard, but when these compositions are reinforced with inorganic reinforcing materials such as glass fibers to enhance their stiffness, the cotton ignition phenomenon occurs at the time of combustion even if the flame-retarding agents are added in a large amount, and thus they do not meet the requirements of the UL94V-0 standard.
On the other hand, there have been proposed a flame retarding technique which is free from halogen and which uses intumescent type flame-retarding agents such as melamine phosphate, melamine pyrophosphate and melamine polyphosphate in glass fiber-reinforced polyamide resins (JP-A-10-505875), and a technique of adding melamine polyphosphate to polyamide resins reinforced with inorganic materials and further using a charring catalyst and/or a char forming agent (WO98/45364). It is known that moldings thereof having a thickness of {fraction (1/16)} inch meet the requirements of the UL94V-0 standard. However, according to these techniques, melamine phosphate-based flame-retarding agents must be used in large amounts in order that thin-wall moldings of {fraction (1/32)} inch thick, which are especially demanded for uses as connectors of electric and electronic parts, meet the requirements of the UL94V-0 standard. When the melamine phosphate-based flame-retarding agents are used in large amounts, not only are the glass fiber-reinforced polyamide resin compositions seriously deteriorated in mechanical characteristics, but also they are inferior in electric characteristics, particularly, tracking resistance which is required for electric parts used under high voltage environments. Moreover, when the melamine phosphate-based flame-retarding agents are used in large amounts, releasability from the mold at the time of molding is inferior, and, furthermore, molding for a long period of time at high molding temperatures is apt to cause corrosion of the mold. Thus, the compositions are not necessarily satisfactory as molding materials for electric and electronic parts.
Furthermore, there is disclosed a technique of applying melamine sulfate which is an intumescent type flame-retarding agent to glass fiber-reinforced half-aromatic polyamide resins for meeting the requirement of the UL94V-0 standard as thin-wall moldings of {fraction (1/32)} inch thick (JP-A-2000-11951), but this technique also requires the addition of the flame-retarding agent in a large amount for the amount of the polyamide resin component, and suffers from the same problems as above.
Moreover, as a technique for imparting a high tracking resistance which meets the requirement of the UL94V-0 standard as thin-wall moldings of {fraction (1/32)} inch thick, there is proposed a technique of adding a melamine phosphate composite flame-retarding agent and an alkaline earth metal salt to inorganic material-reinforced polyamide resins (WO00/09606), but moldings obtained by this technique are brittle, and when applied to, for example, connectors having complicated shapes, there are problems that the connectors are broken or cracked during handling or transportation.
The object of the present invention is to provide a flame retardant reinforced polyamide resin composition which is very high in flame retardancy, does not generate hydrogen halide gases having corrosiveness at the time of combustion and has both excellent electric characteristics and excellent molding processability.
As a result of intensive research conducted by the inventors, it has been found that the above object can be attained by using a half-aromatic polyamide resin having a specific structure as a polyamide resin in a system comprising a combination of an inorganic reinforcing material, a melamine polyphosphate and a polyamide, and thus the present invention has been accomplished.
That is, the present invention is directed to a flame retardant reinforced polyamide resin composition comprising (a) 30-70% by weight of a half-aromatic polyamide resin having a hexamethylene adipamide unit and a hexamethylene isophthalamide unit, (b) 10-38% by weight of a melamine polyphosphate and (c) 5-50% by weight of an inorganic reinforcing material.
Furthermore, if necessary, the flame retardant reinforced polyamide resin composition of the present invention may further comprise (d) 0-5% by weight of a polyalkylene polyhydric alcohol and/or a fatty acid ester derivative thereof, (e) 0-5% by weight of a bisamide compound, (f) 0-5% by weight of a metal oxide and/or a molybdate, and (g) 0-5% by weight of a metal salt of a higher fatty acid having 10-25 carbon atoms in addition to the above components (a)-(c).
Moreover, in the flame retardant reinforced polyamide resin composition of the present invention, it is preferred that the ratio of amounts of the half-aromatic polyamide resin and the melamine polyphosphate is in the range of 1.5-3.5.